Air-compressor



B. D. THOMPSON. AIR COMPRESSOR.

APPLICATION FILED MAR 11. I919.

Patented July 6, 1920.

UNITED STATES BUBGHARD D. THOMPSON, OF CYCLONE, PENNSYLVANIA.

AIR-COMPRESSOR.

Specification of Letters Patent.

Patented July 6, 1920.

Application filed. March 11, 1919. Serial No. 281.905.

To all whom it may concern:

Be it known that I, BUBOHARD D. THOMP- soN, a citizen of the United States residing at Cyclone, in the county of Mcliean and State of Pennsylvania, have invented certain new and useful Improvements in Air- Compressors, of which the following is a specification, reference being had therein to the accompanying drawing.

This invention relates to improvements in an air compressor, which is more particularly intended to furnish air-pressure for field use.

The primary object of my invention is to sheet elhciency and economy in the operation of an air compressor by associating therewith a tank into which the compressor compresses and forces air, and from which the compressor receives the compressed air to be again compressed and forced into the field line pipe for any desired use.

The accompanying drawing is an elevation of a device embodying my invention, the air compressor features thereof being shown in longitudinal section.

In carrying out my invention, a suitable tubular casing 1 is provided, and this casing is divided into two cylinders 2 and 3,.

by cylinder heads at and 5, which are placed in and fixedly attached within the casing 1 and about its center. While I show these two cylinder heads 4 and 5, I desire it to be understood that these. two heads could be combined into a single head, but 1 prefer to make them separate forconvenience in construction. A piston 6 is within the cylinder 2 and a piston 7 within the cylinder 3, and these two pistons are connected by a large connecting rod or tube 8, which passes through the heads at and 5. These pistons 6 and 7 are reciprocated in their cylinders by any suitable form of reciprocating motive power (not shown) which 1s provided with a reciprocating member 9, preferably carrying a cross-head 10, and this cross-head 10 is connected with the large piston rod 8, by a small ordinary sized piston rod 11, which passes through the end cylinder head 12.

Attached to the outer side of the cylinder casing 1, is a suitable housing 13, which forms a chamber 1&, and this chamber 1 1 is in communication with a suitably sized tank 15, by a pipe 16.

municating respectively with the cylinder 2 and with the chamber 14: of the housing 13, and the port 18 having one end communicating with the cylinder 2, and its opposite end communicating with a pipe 19. Likewise the inner cylinder head 5 is provided with the ports 20 and 21, one end of the port 20 communicating with the cylinder 3, and its opposite end with the chamber 1%, while one end of the port 21 communicates with the cylinder 3, and its opposite end with a pipe 22. These pipes 19 and 22 are connected with the field line pipe 23.

The ports 17, 18, 20 and 21 are controlled by a suitable valve 24, which may be of any desired type without affecting my present invention, so long as it will performthe function hereinafter described. The form of valve here shown is of the reciprocating type and it has at one end a port 25, adapted to alternately control the ports 17 and 18, and at its opposite end a port 26, which is adapted to alternately control the ports 20 and 21. A valve operating rod 27 has one end connected with the valve 24:, and its opposite end loosely passing through suitable supports 28 carried by the cross-head 10. This valve rod 27 is provided with two adjustable stops 29 and 30, which are engaged by the supports 28 of the cross-head 10, as it reciprocates. lVith the ports in the position here shown, the pistons have reached their limit of movement in' the direction indicated by arrow, and the support 28 has engaged the stop 30 and moved the valve 2% to the position shown. When the pistons 6 and 7 have reached their limit of movement in the other direction of movement, the support 28 will have engaged the stop 29 and pushed the valve 24 in the opposite position to that here shown, which will open the ports 17 and 21, and close the ports 18 and 20, which are shown open in the position of the valve illustrated.

Owing to the large connecting rod8 be tween the pistons 6 and 7 it will be observed that the cubic capacity of the spaces between the pistons and the heads 4 and 5 is less than the cubic capacity between the pistons 6 and 7, and the heads 12 and 12 of the cylinder casing. From this it follows that a greater amount of air is taken into the cylinders at the outer sides of the pistons 6 and 7 than can enter the cylinders at the opposite or innersides of the pistons 6 and 7.

The cylinder casing heads 12 and 12 are each provided with inlet openings 31 and 32, which are provided with suitable check valves 33, which permit air to be drawn In the operation of the compressor'air is' taken into the outer ends of the cylinders 2 and 3 through the inlet openings 31 and 32 at atmospheric pressure. lVith the partsin the positions here shown, the compressed air is being forced from the tank 15 into the cylinder 3, at the inner side of the piston 7 and there is a higher air pressure at the inner side of the piston 7 than at the outer side. lVith the pistons 6 and.7 moving in the direction indicated by the arrow a,'the compressed air which flowed from the tank 15, through the ports 17 to the inner side of the piston 6, is again compressed and is forced therefrom through the port 18 into the pipe 19 and thence to the field line pipe 23, and air is drawn through the inlet 31 at atmospheric pressure filling the cylinder 2 at the outer side of the piston 6. When the piston 6 has reached the inner'limit of its movement, the valve 241 is shifted, as hereinbefore explained, which will close the ports 18 and 20 and open the ports 17 and 21. This reversal of the valve 21 establishes communication between the tank 15 and the inner side of the piston 6, so that compressed air flows from the tank into the cylinder at a much greater pressure than the atmospheric pressure at the outer side of the piston 6.

From this construction it will be observed that owing to the relatively larger cubic capacity of the cylinders at the outer sides ofthe pistons 6 and 7, a greater amount of air is forced into thetank than flows therefrom into the relatively smaller cubic capacities of the cylinders 2 and 3, at the in-' ner sides of the pistons 6 and 7.

From the foregoing description it will be observed that air is alternately flowing from the tank 15 into the cylinders 2 and 3, at the inner side of the pistons 6 and 7, and alternately being compressed therein and forced into the field line pipe 23. Likewise air is being alternately drawn into the cylinders 2 and 3, at the outer sides of the pistons 6 and 7, and alternately compressed therein and forced into the tank 15.

By reason of the foregoing construction a high air pressure is maintained in the tank 15 and the construction will maintain a higher pressure in the tank 15 than is maintained in the field line pipe 23. For illustration, we will suppose the air in the tank 15 to be at 160 pounds pressure and the air in the field line pipe 23 at pounds pressure. This leaves a margin of 90 pounds pressure to flow from the tank 15 to the cylinders 2 and 3 at the inner sides of the pistons 6 and 7, as before explained. This arrangement provides for a double compression of the air before it is forced into the field line pipe 23, where-it travels against the friction of the field line pipe from which it is being drawn'for use thus lowering it in the hypothetical statement herein given to approximately 7 0 pounds. By utilizing the tank and the structure here shown to increase therein a greater pressure, the pressure taken from the tank into the cylinder serves to equalize the compressing capacity of the compressor. For the purpose of conveying excess pressure from the tank 15 to the field line pipe 23, I provide a connection 37 between the tank 15 and the field line pipe 23, and this connection is provided with any suitable type of pressure releasing valve 38, so that when the pressure in the tank is above a predetermined degree, it will open the pressure valve 38 and flow through the connection 37 to the field line pipe 23. F or the purpose of preventing excess pressure in the tank exploding it, I provide any, suitable type of puppet or safety valve 39,

through which excess pressure will flow off,

and I provide a second similar pressure relief valve 40 in communication with the tank 15, through a pipe 41. s

The construction of the valves 38, 39 and 410 form no part of my present invention and are not specifically shown, 'as any wellknown type of valve can be utilized. This is equally true in respect to the check valves 33 and 36.

While I have shown two cylinders 2 and 3, I desire it to be understood that a single cylinder could be utilized to carry out the inventive idea of having the compressed air from the tank 15 alternately flow into the cylinder to be compressed a second time and forced into the field line pipe.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

An air compressor comprising a cylinder casing having an intermediate cylinder head forming two cylinders, a piston in the said cylinder, an operating piston rod passing through one of the outer heads of the cylinder and connected with the adjacent piston,

two pistons and reciprocating through the inner cylinder head, the outer ends of each cylinder having air inlets, a tank communicating with the outer ends of the cylinders, the inner cylinder head having two sets of inlet and outlet ports, and means for controlling the said ports by opening the inlet port when its respective piston is moving away from the port and closing the outer port, and opening its respective outlet port and closing its respective inlet port when 10 the piston is moving toward the said orts.

In testimony whereof I hereunto a my signature.

BURCHARD D. THOMPSON. 

